Temperature sensor

ABSTRACT

A temperature sensor suitable for use in an electrically heated, laminated window is disclosed. The laminated window includes a plastic interlayer material sandwiched between two rigid, transparent sheets, one of which sheets has an electrically conductive coating in contact with the interlayer. Embedded within the plastic interlayer is the temperature sensor which is comprised of a resistance filament encapsulated within a substantially material which has a heat deflection temperature greater than the plastic interlayer. Because the temperature sensor has a casing with a higher heat deflection temperature than the plastic interlayer into which it is embedded, fracture and shorting of the resistance filament against the electrically conductive coating, during the high temperature and high pressure conditions of laminating, are avoided. In a particular embodiment of the invention where the interlayer material is plasticized, a protective layer disposed between the interlayer and casing material to prevent hazing is disclosed.

United States Patent [191 Spindler TEMPERATURE SENSOR [75] Inventor:Robert G. Spindler, Allison Park,

[73] Assignee: PPG Industries, Inc., Pittsburgh, Pa.

[22] Filed: Sept. 1, 1972 [21] Appl. No.: 285,779

Related US. Application Data [63] Continuation-in-part of Ser. No.199,221, Nov. 16,

1971, abandoned.

[52] US. Cl 338/24, 161/183, 219/203, 219/494, 219/522, 219/544,338/270, 338/301 [51] Int. Cl 1101c 7/10 [58] Field of Search...219/203, 494, 501, 504, 522, 219/543, 544; 338/23, 20, 21, 22, 253, 270,297, 24, 301, 25; 161/183, 190, 199; 73/362 [56] References Cited UNITEDSTATES PATENTS 2,178,548 11/1939 Black et a1 338/24 2,407,288 9/1946Kleimack et a1 338/23 3,697,863 10/1972 Kilner 338/24 X 2,644,065 6/1953Peterson 219/522 X 2,806,118 9/1957 Peterson 219/203 3,356,833 12/1967Orcutt 219/522 1,476,116 12/1923 Thompson 338/301 X 3,020,376 2/1962Hofmann et al. 219/203 3,330,942 7/1967 Whitson 219/522 3,388,032 6/1968Saunders 161/183 3,532,590 10/1970 Priddle 161/183 Jan. 29, 1974 j3,539,442 11/1970 Buckley et a1. 161/183 3,551,873 12/1970 Weyenberg338/253 3,622,440 ll/l971 Snedeker et al. 161/193 PrimaryExaminer-Volodymyr Y. Mayewsky Attorney, Agent, or Firm-Edward I. Mates;William J. Uhl

57 ABSTRACT tic interlayer is the temperature sensor which is comprisedof a resistance filament encapsulated within a substantially materialwhich has a heat deflection temperature greater than the plasticinterlayer. Because the temperature sensor has a casing with a higherheat deflection temperature than the plastic interlayer into which it isembedded, fracture and shorting of the resistance filament against theelectrically conductive coating, during the high temperature and highpressure conditions of laminating, are avoided. In a particularembodiment of the invention where the interlayer material isplasticized, a protective layer disposed between the interlayer andcasing material to prevent hazing is disclosed.

12 Claims, 6 Drawing Figures PATENIED JAN 2 9 I974 SHEEI 1 OF 2TEMPERATURE sENsoR CROSS REFERENCE TO RELATED APPLICATIONS Thisapplication is a continuation-in-part of copending application Ser. No.199,221, filed Nov. 16, I971, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention:

This invention relates to a temperature sensor for use in laminated,electrically heated glass-plastic windows.

2. Description of the Prior Art:

Electrically heated, laminated windows have been known for some time.Such windows find wide use where it is necessary that vision through thewindows be kept free of ice and fog formations. This is particularlytrue in aircraft, in which the windows are frequently subjected tovarious and extreme weather conditions. A typical electrically heated,laminated window is one which includes two outer sheets of glasslaminated to a plastic interlayer. One of the glass sheets has anelectrically conductive coating, for example, a transparent metal oxidefilm, which contacts the plastic interlayer. Power'is supplied to thefilm by electrodes or bus bars which are positioned around the marginaledges of the film and which are in electrical contact with theelectrically conductive coating. To regulate the power supplied to thecoating, and thus control the temperature of the window, temperaturesensors are embedded in the plastic interlayer. The temperature sensorsare usually resistance filaments which vary in resistance according tothe surrounding temperature.

A typical and widely used temperature sensor is that disclosed in U. S.Pat. No. 2,644,065 to Peterson, which consists of a resistance filamentencapsulated within a polyvinyl butyral casing. The sensor is insertedinto an opening cut out of the polyvinyl butyral interlayer, and whenthe window is laminated during a high temperature autoclaving step, thetemperature sensor blends with the polyvinyl butyral interlayer so as toform an integral part of the window. The temperatures needed forlaminating the polyvinyl butyral interlayer to the outer glass sheetsmust be sufficient to soften the polyvinyl butyral. During lamination,the polyvinyl butyral flows and wets the glass, producing a strongglasspolyvinyl butyral bond. Unfortunately, this flowing at timesfractures the fine resistance filaments which are embedded within thepolyvinyl butyral, and at times shorts the resistance filament againstthe electrically conductive coating. Therefore, it is an object of thisin vention to provide a temperature sensor of the resistance filamenttype which can be pressed into a plastic interlayer, particularlypolyvinyl butyral, during lamination without the dangers of filamentfracture, or of filament shorting with the electrically conductivecoating.

Many of the commercially available polyvinyl butyral interlayers areplasticized to improve their flexibility and impact resistance. Theplasticizers are generally water-insoluble esters of a polybasic acidand a polyhydric alcohol. Unfortunately, when a temperature sensor isencased in a casing material which is different than the surroundingpolyvinyl butyral, it is believed that these plasticizers have atendency to migrate to the surface of the casing material and cause itto become hazy. This is especially troublesome when the casing is apolycarbonate and when the interlayer material is plasticized polyvinylbutyral. Although the temperature sensor casing is hazy, it stillfunctions as intended, but it is unsightly looking in the resultantlaminated window.

It is therefore a further object of this invention to provide means toinhibit the formation of haze in the casing of a temperature sensorwhich is embedded into a plasticized plastic interlayer, particularlyplasticized polyvinyl butyral.

SUMMARY OF THE INVENTION According to this invention, there is provideda temperature sensor principally for use in an electrically heated,laminated window. The sensor includes a resistance filament encapsulatedwithin a casing which has a higher heat deflection temperature than thatof the plastic interlayer into which the sensor is embedded. In analternate embodiment of the invention, a protective layer is disposedbetween the interlayer and the casing. The protective layer is used whenthe interlayer material is plasticized and would cause the casing tobecome hazy if placed in contact with it. When the temperature sensor islocated in a vision portion ofa window, the casing is preferablytransparent and so is the protective layer, if used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows perspectively a constanttemperature laminated window system containing the temperature sensor ofthis invention,

FIG. 2 is a cross-sectional view through II-II of FIG.

FIG. 3 is a plan view of the temperature sensor of the invention,

FIG. 4 is an exploded view, depicting the construction of thetemperature sensor element of the invention, and

FIGS. 5 and 6 are exploded views, depicting the construction of thetemperature sensor element of this invention in two alternateembodiments.

DETAILED DESCRIPTION FIGS. 1 and 2 depict a constant temperaturelaminated window system. The system comprises a transparent, laminated,electrically heated window 1. The window includes two rigid, transparentsheets 3 and 5, one of which has an electrically conductive coating 13thereon. The coating is operatively connected through electrodes 15 andthrough a control system or control- Ier 27 to a source of electricalenergy 19. The source of electrical energy 19 will depend on the windowsapplication. For a heated aircraft window, for example, the source ofelectrical energy 19 would be an alternator driven by an aircraftengine. Sandwiched between the two rigid, transparent sheets 3 and 5 isa transparent interlayer which comprises a plurality, 7, 8, 9 and 11, ofplastic laminae. As is shown in the drawing, the plastic interlayer alsocontacts the electrically conductive coating 13. Embedded within theplastic interlayer is a temperature sensing element 21 which is shown insomewhat more detail in FIGS. 3 and 4.

Temperature sensor 21 comprises a resistance filament 23 encapsulatedwithin a casing 25 which has a heat deflection temperature greater thanthe plastic interlayer material into which the temperature sensor 21 isembedded. The temperature sensor 21 is operative'ly connected to thesource of electrical energy 19 through a controller 27. In operation,the temperature sensing element 21 responds to changes in temperatureappurtenant the window 1 and in so responding, modifies, through theactivity of the controller 27, the source of electrical energy so as tomaintain the temperature of the window at a predetermined range. Thecontroller 27 modifies the output voltage applied by the source ofelectrical energy 19. For a description ofa typical controller, see U.S. Pat. No. 2,806,] 18 to Peterson.

Alternate embodiments of the invention are shown in FIGS. 5 and 6.Briefly, the alternate embodiments show the disposition of a protectivelayer about the casing. The protective layer can be composed of twosheets 60 and 61 which are adhered to the casing. The alternateembodiments shown in FIGS. 5 and 6 will be described in detail below.

LAMINATED WINDOW Referring once again to FIGS. 1 and 2, the laminatedwindow 1 includes two rigid, transparent outer plies 3 and 5 of the sameor different thickness, each thickness being approximately 0.080 tol.000 inch. Either one or both of the plies are either a rigid, plasticmaterial, like polycarbonate or acrylic sheeting, or a flat glass sheet,with glass being preferred. A transparent plastic interlayer having athickness of 0.060 to 0.500 inch is sandwiched between the outer plies 3and 5 and includes a plurality of laminae of plastic, 7, 8, 9 and 11,formed of polyvinyl butyral or other suitable plastic interlayermaterial well known in the art, such as polyurethane. Polyvinyl butyralinterlayer materials are described in U. S. Pat. Nos. Re. 20,430 toMorrison, 2,372,522 to Strauss and 2,496,480 to Lavin et al.Polyurethane interlayer materials are described in U. S. Pat. Nos.3,509,015 to Wismer et al. and 3,620,905 to Abramjian. Four plies ofplastic are shown in FIGS. 1 and 2, but it should be understood thatmore or less than four plies can be used, depending upon therequirementsthe window will have to meet, An opening is provided in the interlayerof a size equal to that of the temperature sensing element 21. Theelement is inserted within the opening, and the individual components ofthe window are assembled and are laminated together such that thetemperature sensor blends with the plastic interlayer so as to form anintegral part of the window. As is shown in FIGS. 1 and 2, thetemperature sensing element 21 is embedded in the plastic interlayer andis approximately 0.010 to 0.060 inch from the electrically conductivecoating 13. Lead wires 39 and 40 are brought out from the element 21between the plastic layers 8 and 9 to the controller 27.

Between the rigid, transparent outer ply 3 and the plastic interlayer isan electrically conductive, transparent coating 13, such as a metaloxide film of the type described in' U. S. Pat. No. 2,614,944 to Lytle.Electrically conductive coated glass of this type is sold commerciallyunder the trademark NESA. The coatings have a thickness of about 50 to3500 millimicrons and are substantially transparent. (Thickness of thecoating 13 in FIG. 2 is exaggerated for the purpose of illustration.)When an electrical potential is applied across the coating, theelectrical resistance of the coating causes it to give off heat.Generally, the electrical resistance of the coatings are below about 500ohms per unit square, and have a specific resistivity below about 0.002ohms-centimeters. Other transparent conductive materials, such as goldcoatings and other thin metal coatings, may be used as the electricallyconductive, transparent coating.

To bring electricity to the coating 13, electrodes 15,

commonly called bus bars, are provided along a pair of opposed marginaledges of the coating. The bus bars 15 comprise a highly conductive metalpowder, preferably gold or silver, and a vitrifying binder. Bus bars arewell known in the art and are typically described in U. S. 7

TEMPERATURE SENSOR The temperature sensing element 21 is shown in detailin FIGS. 3 and 4. It includes a resistance filament 23 encapsulatedwithin a casing material 25 which has a higher heat deflectiontemperature than the plastic interlayer material into which thetemperature sensor 21 is embedded.

in the following specific description of the temperature sensor 21, thecasing material is described as being polycarbonate. However, it shouldbe realized that other plastic materials could be used instead ofpolycarbonate. The selection of a casing material will depend on theinterlayer material into which the temperature sensor is embedded. Moreparticularly, the selec tion of the casing material will depend on thelaminating temperatures and pressures which soften the interlayer,causing it to flow and wet the glass to form a strong glass-interlayerfusion bond. The casing material should not soften and flow at thesetemperatures, at least to an extent which will cause fracture of theencapsulated resistance filament, or which will cause shorting of thefilament against the electrically conductive coating. An indication ofthe temperatures and pressures which will cause a material to soften andto flow is reflected in the heat deflection temperature of the material.The heat deflection temperature of plastics is defined as themeasurement of the temperature at which a specific load will cause aplastic to deflect a specified amount. Procedures for determining heatdeflection temperatures of plastics are set forth in A.S.T.M. 13-648.

According to this invention, the casing should be selected fromthose'materials which have a higher heat deflection temperature than theplastic interlayer into which the temperature sensor is embedded. It isalso preferable that the casing be transparent, having an index ofrefraction similar to the interlayer, such that when the two are pressedtogether in the resultant laminated window, the casing of thetemperature sensor will not be distractingly noticeable.

By far the most widely used plastic interlayer material is polyvinylbutyral which has a heat deflection temperature of ll5-165F. at '66 psias measured by A.S.T.M. 13-648. Polycarbonate has been found to beespecially useful as a plastic casing material for the temperaturesensor with polyvinyl butyral, because polycarbonate is transparent andhas an A.S.T.M. D 648 heat deflection temperature of 270290F. at 66 psi.However, it should be appreciated that other transparent plasticmaterials for use as casing materials having a higher heat deflectiontemperature than polyvinyl butyral could be used. Also, if the plasticinterlayer material is other than polyvinyl butyral, the plastic casingmaterial can be selected from those plastics which will have a higherheat deflection temperature than the plastic interlayer material chosen.

As shown in FIG. 4, the temperature sensing unit 21 comprises apolycarbonate core section 41. The core section has a thickness of about0.003 to 0.030 inch. The polycarbonate core section 41 includes a thinpolycarbonate card 43, around which a resistance filament 23 isuniformly looped. Surrounding the card are a plurality of polycarbonatespacers 47 to eliminate any lens effect which may result when thevarious components of the temperature sensor 21 are laminated together.Located on the card 43 are weld tabs 51 which connect the resistancefilament 23 with the lead wires 39 and 40. The core section 41 isencapsulated between two sheets of polycarbonate 54 and 55 by a hightemperature-pressure cycle, for example, a cycle in an autoclave or aplaten press. Temperatures of about 275390F. and pressures of about25-250 psi for about five to 120 minutes are suitable to form thetemperature sensing unit 21 as depicted in FIGS. 3 and 4.

The casing 25 (which includes the core section 41) is chosen from thosematerials which will not cause the encapsulated resistance filament tofracture or to short against the electrically conductive coating duringthe laminating of the window 1. Accordingly, the casing material shouldhave a heat deflection temperature greater than the plastic interlayermaterial into which it is embedded. During the high temperatures andpres sures which are needed in the lamination step to bond theinterlayer material to the outer rigid, transparent plies, theinterlayer material softens and flows. The casing material, because ithas a higher heat deflection temperature than the surrounding interlayermaterial, does not flow, remains stable and will not cause fracture orshorting of the encapsulated filament.

When the interlayer material is polyvinyl butyral, which has a heatdeflection temperature of l l5-l 65F. at 66 psi, the casing materialpreferably is polycarbonate, which has a heat deflection temperature of270-290F. at 66 psi. Polycarbonates are described in U. S. Pat. No.3,028,365 to Schnell et al. Polycarbonates are also commerciallyavailable under the trademarks LEXAN and MERLON. Other suitable plasticencapsulating materials for use with polyvinyl butyral are, for example,cast acrylic, which has a heat distortion temperature of 175225F.,polystyrene, which has a heat deflection temperature of 2l0230F.,polyester, which has a heat deflection temperature of 270290F.,polysulfone, which has a heat deflection temperature of 350F. and nylon,which has a heat deflection temperature of 300-400F.

It should be realized that the resistance filament can be looped aboutthe card 43 in any particular manner or configuration. Alternately,-theresistance filament does not have to be looped around a card 43, butcould be merely wound in a spiral or helix configuration and molded byitself into the plastic casing 25. However, it is preferred that theresistance filament 23 be uniformly looped around a card 43. Althoughthe card 43 has a higher heat deflection temperature than the plasticinterlayer, it can be made from a different material than the sheets 54and 55 which form the exposed casing 25. For example, the card 43 (andspacers 47) can be made from polycarbonate and the sheets 54 and 55 fromacrylic. This latter embodiment is preferred as will be explained belowwhen the interlayer material is plasticized polyvinyl butyral.

The resistance filament 23 is a fine wire adapted to have the resistancethereof changed in response to a change in the surrounding temperature.The wire is typically about 0.0005 to 0.002 inch in diameter, having apositive temperature coefficient of resistance and having sufficientelasticity as to permit fabrication of the temperature sensing unit 21and fabrication of the laminated window 1 without breakage and shorting.

The resistance filament should be responsive to temperatures within therannge of -F. to 160F., which is the ambient temperature range oftypically high flying aircraft. In particular, when polyvinyl butyral isthe plastic interlayer material, the resistance filament should be verysensitive to temperature changes around l00l20F., which is thetemperature at which polyvinyl butyral has its greatest impact strength.Preferably, the change in resistance of the filament with tempera tureshould be at least from about to ohms per circular mil foot at 20C.Examples of various materials of construction which can be used to makethe resistance filament are tungsten, nickel, iron-nickel alloys, withan iron and nickel alloy sold under the trademark HYTEMPCO beingpreferred.

The lead wires 39 and 40 should be made of a good electrical conductor,such as copper, and should be firmly attached to the resistance filament23. As shown in FIGS. 3 and 4, the lead wires are soldered to a weld tab51 which, in turn, is soldered to the resistance filament 23. The leadwires are generally larger in diame ter than the resistance filament,having a diameter of from about 0.006 to 0.020 inch.

The weld tabs 51 are selected from electrically conducting materialswhich are well suited for soldering or welding. Materials having lowthermal expansion coefficients, such as a nickel-iron alloy sold underthe trademark KOVAR, are preferred.

Besides the individual components of the temperature sensor 21 havingthe above'described properties, the temperature sensor itself shouldhave certain spe cific design requirements. The temperature sensor unit21 should be capable of withstanding an extended exposure to an ambienttemperature range of -75F. to F., which is the ambient temperature rangeof high flying aircraft. When assembled into an electrically heatedwindow, the temperature sensor should be capable of withstandinglaminating conditions that include pressures as high as 225 pounds persquare inch at temperatures of 70350F. Exposures to these conditions forabout 30 to 120 minutes should not impair the electrical, structural orvisual characteristics of the temperature sensor.

As has been mentioned above, many of the plastic interlayer materialsare plasticized to prevent their eventual embrittlement. Virtually allof the commercially available polyvinyl butyral sheet interlayermaterial is plasticized. For example, polyvinyl butyral for use inaircraft laminates contains 21 parts by weight of monomethoxydiethyleneglycol adipate per 100 parts by weight of polyvinyl butyral. Since thecasing in this invention is a different material than the interlayermaterial, there is a possibility that the plasticizer in the interlayermaterial may be reactive toward the casing material of the temperaturesensor. Such is the case when the casing material is the preferredpolycarbonate, and the interlayer material is the widely usedplasticized polyvinyl butyral. It is believed that the plasticizermigrates from the polyvinyl butyral to the surface of the plasticcasing, interacts with the polycarbonate, causing it to become hazy.This hazing, although not affecting the performance of the temperaturesensor, gives the sensor a distracting, unsightly appearance in the resultant laminated window.

This hazing of the plastic casing can be avoided if a protective layeris positioned about the exterior surface of the casing. In the resultantlaminated window, the protective layer will be disposed between thecasing of the temperature sensor and the interlayer into which thetemperature sensor is embedded.

The protective layer should adhere well to both the plasticizedinterlayer and to the casing material. The protective layer should betransparent, having approximately the same index of refraction as boththe inter layer material and the casing. This minimizes opticaldistortion in the resultant laminated window. Also, the protectivelayer-should not seriously affect the temper ature sensing capabilitiesof the temperature sensor.

An example of a suitable protective layer, when the temperature sensorcasing is polycarbonate and the interlayer material is plasticizedpolyvinyl butyral, is acrylic. In general, acrylics are composedprincipally of one or more of the polymerized lower alkyl esters ofmethacrylic acid, such as methyl methacrylate, ethyl methacrylate,isopropyl methacrylate and isobutyl methacrylate. There may also be usedcopolymers from lower alkyl esters of methacrylic acid or mixtures ofsuch esters in predominant amounts together with lesser amounts ofanother polymerizable unsaturated compound which is miscible orcompatible therewith, such as an ester of acrylic acid; examples ofwhich are ethyl acrylate and butyl acrylate. Acrylics are commerciallyavailable under the trademark KORAD in film and sheet form having athickness of 0.003 to 0.012 inch and are preferred in the practice ofthis invention.

The protective layer can be disposed between the casing of thetemperature sensor and the surrounding polyvinyl butyral in a number ofways. If available in a liquid form, it can be brushed, coated orsprayed onto the casing of the temperature sensor. When applied in thisway, care must be taken to insure that the coating is even to avoid anyoptical distortion. When the protective material is available in film orsheet form, it may be laminated directly to the casing of thetemperature sensor. For example, as shown in FIG. 5, two layers 60 and61 of acrylic are positioned on the exposed outer surfaces of thetemperature sensing element. The composite is then subjected to asuitable high pressure and temperature cycle for lamination. Forexample, when the temperature sensor casing is made from polycarbonateand the protective layer is an acrylic cladding material, such as thatavailable under the trademark KORAD, an autoclaving cycle usingtemperatures of about 250-390F. and pressures of about 25-250 psi forabout five to 60 minutes is suitable to form the resultant protectedtemperature sensing unit. Another way of disposing the protective layerbetween the temperature sensor and the surrounding interlayer materialis to cut a section out of the interlayer material which corresponds tothe size of the temperature sensor. The resistance filament encapsulatedwithin a casing and sandwiched between two protective layers 60 and 6lis then inserted into this opening. The remaining layers of theinterlayers and the rigid outer sheets 3 and 5 are then assembled andprepared for lamination. When the components of the window are laminatedtogether during the high temperature and high pressure autoclaving, thetemperature sensor and protective layer blends with the polyvinylbutyral interlayer so as to form an integral part of the resultantlaminated window.

If the protective material has a higher heat deflection temperature thanthe interlayer material, it can itself be used as the casing material.For example, when the interlayer material is plasticized polyvinylbutyral, it is preferred that the temperature sensor constructioninclude a polycarbonate core section and an acrylic casing.

Depending on the selection of the interlayer material and the casing ofthe temperature sensor, it may be necessary to provide an adhesivebetween the inter layer and the casing to prevent delamination. Careshould be taken, of course, that the adhesive not attack the interlayeror the casing causing haziness or optical distortion. For example, whenthe interlayer material is plasticized polyvinyl butyral and the casingor the protective coating for the casing is an acrylic cladding, apolyurethane adhesive is suitable. Preferred polyurethanes are thethermoplastic type such as are disclosed in U. S. Pat. Nos. 2,871,218and 2,899,411, both to Schollenberger and which are sold under thetrademark TUFTANE. The thermoplastic polyurethanes are available in filmand sheet form, having thicknesses of 0.001 to 0.20 inch.

The adhesive can be inserted between the interlayer and the casing in anumber of ways. If available in liquid form, it can be brushed, coatedor sprayed onto the casing of the temperature sensor. When available insheet or film form, the adhesive foil can be laminated directly to theprotected casing of the temperature sensor. For example, as is shown inFIG. 6, two layers and 71 of a suitable adhesive such as polyurethanefilm are positioned on the exposed outer surface of an acrylic cladtemperature sensor. The acrylic clad temperature sensor and thepolyurethane protective layers are then subjected to a suitable hightemperaturepressure cycle to laminate the polyurethane to the acryliccladding. For example, temperatures of about 250-390F. and pressures ofabout 25l00 psi for about five to 60 minutes are suitable to laminatethe polyurethane to the acrylic. Another way of inserting an adhesivebetween a protectively clad temperature sensor casing and interlayer isto cut a section out of the interlayer material which corresponds to thesize of the temperature sensor. A composite, as is shown in FIG. 6,generally comprising a temperature sensor with a polycarbonate casing,two acrylic protective foils 60 and 61, and two polyurethane adhesivelayers 70 and 71, is inserted into the opening. The remaining laminae ofthe interlayer and the rigid outer sheets 3 and 5 are then assembled andprepared for lamination. When the components of the window arelaminatedtogether during high temperature and high pressure autoclaving, theprotected temperature sensor blends with the 'polyvinyl butyralinterlayer so as to form an integral part of the resultant laminatedwindow.

What is claimed is:

l. A temperature sensor for use with a transparent, laminated,electrically heated window assembly, and which is adapted to be embeddedin a plastic interlayer material, comprising:

a. a resistance filament having a resistivity that changes withtemperature,

b. a transparent casing of a plastic material which has a higher heatdeflection temperature than the plastic interlayer, said filament beinghermetically encapsulated within said casing, and

c. electrical leads extending through said casing and adapted to connectsaid resistance filament to a control system.

2. A temperature sensor as set forth in claim 1, in which the casingmaterial is polycarbonate.

3. A temperature sensor as set forth in claim 1, in which a protectivelayer is disposed between said casing and said interlayer.

4. A temperature sensor as set forth in claim 3, in which the protectivelayer is acrylic.

5. A temperature sensor as set forth in claim 3, in which the protectivelayer comprises an outermost layer of polyurethane and an interlayer ofacrylic.

6. A temperature sensor as described in claim 1, in which the casingmaterial is selected from the class consisting of polycarbonate, castacrylic, polystyrene, polyester, polysulfone and nylon.

7. A temperature sensor as set forth in claim 6, in which the resistancefilament is uniformly looped about a polycarbonate card andpolycarbonate spacers are positioned around said card tohermeticallyencapsulate said card within said casing.

8. A temperature sensor as set forth in claim 7 in which the casingmaterial is acrylic.

9. A temperature sensor as set forth in claim 8 in which a polyurethaneadhesive is disposed about the 10 acrylic casing.

10. A temperature sensor for use with a transparent, laminated,electrically heated window assembly comprising:

a. a resistance filament having a resistivity that changes withtemperature uniformly looped about a polycarbonate card,

b. a transparent polycarbonate casing, said card being hermeticallyencapsulated within said casing, and

0. electrical leads extending through said casing and adapted to connectsaid resistance filament to a control system.

11. A temperature sensor for use with a transparent, laminated,electrically heated window assembly comprising:

a. a resistance filament having a resistivity that changes withtemperature uniformly looped about a polycarbonate card,

b. a transparent acrylic casing, said card being hermeticallyencapsulated within said casing, and

c. electrical leads extending through said casing and adapted to connectsaid resistance filament to a control system.

12. A temperature sensor for use with a transparent, laminated,electrically heated window assembly comprising:

a. a resistance filament having a resistivity that changes withtemperature,

b. a transparent casing of a transparent plastic material which has aheat deflection temperature higher than that of polyvinyl butyral, saidfilament being hermetically encapsulated within saidcasing, and

c. electrical leads extending through and adapted to connect saidresistance filament to a control system.

UNITED STATES PATENT OICFFICE CERTIFICATE OF CGECTION Patent No. 2 3 191Dated January 29 1974 Inventor(s) Robert G. Spindler It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In the Abstract, line 9, "substantially" should be -casing.

Column 6, line 18, "rannge" should be -range-.

Claim 12, Column l0, line 34 after "through" insert said casing--.

Signed and sealed this 9th day of April 197A.

(SEAL) Attest:

EDWARD M .FLETCHER,JR G MARSHALL DAMN Attesting Officer Commissioner ofPatents FORM PO-105O (10-69) uscoMM-Dc 60876-P69 U.S. GOVERNMENTPRINTING OFFICE: I919 O-SGUJJI,

CERTlFICATE OF CEC'HGN Patent No. Q 191 Dated January 29, 1974Inventor-(s) Robert G. Spindler It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

In the Abstract line 9, "substantially" should be casing--.

Column 6, line 18, "rannge" should be -'-range-.

Claim 12, Column 10, line 34 after "through" insert --said casing-Signed and sealed this 9th day of April 1971;.

(SEAL) Attest:

EDWARD M .FIETCHER, 531., C MARSHALL DAMN Attesting Officer Commissionerof Patents F ORM PC1-1050 (10-69) USCOMM-DC 60376-P69 W .5. GOVERNMENTPRINTING OFFICE l5, 0-358SJM

2. A temperature sensor as set forth in claim 1, in which the casingmaterial is polycarbonate.
 3. A temperature sensor as set forth in claim1, in which a protective layer is disposed between said casing and saidinterlayer.
 4. A temperature sensor as set forth in claim 3, in whichthe protective layer is acrylic.
 5. A temperature sensor as set forth inclaim 3, in which the protective layer comprises an outermost layer ofpolyurethane and an interlayer of acrylic.
 6. A temperature sensor asdescribed in claim 1, in which the casing material is selected from theclass consisting of polycarbonate, cast acrylic, polystyrene, polyester,polysulfone and nylon.
 7. A temperature sensor as set forth in claim 6,in which the resistance filament is uniformly looped about apolycarbonate card and polycarbonate spacers are positioned around saidcard to hermetically encapsulate said card within said casing.
 8. Atemperature sensor as set forth in claim 7 in which the casing materialis acrylic.
 9. A temperature sensor as set forth in claim 8 in which apolyurethane adhesive is disposed about the acrylic casing.
 10. Atemperature sensor for use with a transparent, laminated, electricallyheated window assembly comprising: a. a resistance filament having aresistivity that changes with temperature uniformly looped about apolycarbonate card, b. a transparent polycarbonate casing, said cardbeing hermetically encapsulated within said casing, and c. electricalleads extending through said casing and adapted to connect saidresistance filament to a control system.
 11. A temperature sensor foruse with a transparent, laminated, electrically heated window assemblycomprising: a. a resistance filament having a resistivity that changeswith temperature uniformly looped about a polycarbonate card, b. atransparent acrylic casing, said card being hermetically encapsulatedwithin said casing, and c. electrical leads extending through saidcasing and adapted to connect said resistance filament to a controlsystem.
 12. A temperature sensor for use with a transparent, laminated,electrically heated window assembly comprising: a. a resistance filamenthaving a resistivity that changes with temperature, b. a transparentcasing of a transparent plastic material which has a heat deflectiontemperature higher than that of polyvinyl butyral, said filament beinghermetically encapsulated within said casing, and c. electrical leadsextending through and adapted to connect said resistance filament to acontrol system.